Newsgroups: comp.parallel.mpi
From: guptavi1@cps.msu.edu (Vivek Gupta)
Subject: Clarifications on Ready/Sync modes
Organization: Michigan State University
Date: 12 Aug 1995 01:11:40 GMT
Message-ID: <40gv4c$r71@msunews.cl.msu.edu>

Hi,

I wish to have some clarifications about the various send modes provided by
MPI. Especially, I am not sure if I have understood the ready mode well.

a) For the synchronous mode, can the send complete as soon as a matching 
   receive is posted OR is it necessary that the matching receive should have 
   "got/received some data" ? I believe the former is true since for a non-
   blocking sync-send can be matched by a non-blocking receive call.

b) For the ready mode, shouldn't the send be started only when the matching
   receive gets posted. That implies that the receiver will need to send
   a message like RECV-POSTED/READY to the sender. The "Advice to 
   implementors" (Section 3.4), however, suggests that in ready mode, a 
   message is sent "as soon as possible". Also it suggests that ready send can
   be implemented as a standard send...but then isn't it possible that the std
   send might complete even without a receive getting posted.

   Again the "Advice to Users" in section 3.7 mentions that while use of 
   non-blocking sends in standard and synchronous modes can have a lot of
   impact, the same doesn't hold for the ready mode.

   In my view, since ready can be started only after posting of matching
   receive, it is more similar to synchronous mode and its non-blocking
   version should also be pretty different from the blocking one.
   

Thanks

Vivek
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Dept. of Computer Science, Michigan State University	Ph : (517) 333-4223.
Email : guptavi1@cps.msu.edu    	http://web.cps.msu.edu/~guptavi1/

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